As I am planning on a similiar hunt - I have been asking the same questions you are posing.
Obviously, I can't answer your question about what the pro's and con's are for bivy hunting Elk as I don't know what you consider a successful hunt. For $.02 - I can give you my questions/thoughts on the subject.
First, there is an amazing amount of information, based on other people's experience, available on the Internet. Some of it is in forum's (like this one) - a lot is available on sites like the Colorado Division of Wildlife, GMUResearch, ElkCamp, Basspro, Colorado Bowhunters Association, and about a 1,000 sites advertising guide services.
Are you prepared to get your Colorado Hunter Safety card - if you were born after 1/1/1949 - you will need one. If you don't have a Hunter Safety card from your home state - I suspect you will spend your first day in Colorado in a hunter safety class.
It sounds like there will be two or maybe three of you. What happens if one of you gets an Elk on the first day - say 5 miles from the truck? Are you prepared to field dress it and gets hundreds of pounds of hide, antlers, head, and meat to the truck? What happens after the elk is in the truck - do all of you go to the processor? If not - is the one who didn't get an elk prepared to wait until the other returns - knowing that means they don't hunt until the elk is in the processor? Or are they prepared to hunt by themselves? To make it more interesting - what happens if both of you get an elk? How are you going to get that processed elk home?
The issue of bears was already raised - how about the terrain - are you ready, physically and mentally, for high country? For instance - it is my understanding that summer storms (thunder and snow) at altitude are common, typically violent, and potentially lethal.
Do you have the equipment to handle the range of conditions possible during the summer in Colorado?
How good is everyone in your party with a map/compass and GPS?
Per GMUResearch - there were 557 OTC bowhunters in GMU 65 in 2007 - they took 75 elk. That is a 14% success ratio. Does that work for you or will the hunt be a negative if no one scores?
Looking at the map for GMU 65 available from Colorado Division of Wildlife - the summer range for elk consists of pockets throughout the GMU - have you decided which ones to hunt?
I see you are from from Troy, Il - does that mean you won't be able to do any pre-season scouting? You mention that you might have local knowledge available - are you "Internet scouting" via any of various map sites? There are any number of sites that provide info on how to that - ElkCamp and GMUResearch - come to mind.
What are your limits with your chosen bow/arrow setup? Do you have the ability to get within that range of an elk - by stalking or by calling?
For what it is worth - on all the questions except for those involving physical/mental readiness - my answers to those questions lead to my decision to book a guided hunt rather than trying to DIY.